Thin film deposition and etching techniques are used in semiconductor wafer processing to build interconnects, plugs, gates, capacitors, transistors or other microfeatures. Thin film deposition and etching techniques are continually improving to meet the ever increasing demands of the industry as the sizes of microfeatures decrease and the number of microfeatures increases. As a result, the density of the microfeatures and aspect ratios of depressions (e.g., the ratio of the depth to the size of the opening) are increasing. Thin film techniques accordingly strive to consistently produce highly accurate processing results. Many etching and deposition processes, for example, seek to form uniform layers or other layers that uniformly cover sidewalls, bottoms and corners in deep depressions that have very small openings.
Plasma enhanced chemical vapor deposition and plasma etching are widely used thin film deposition techniques. In these processes energy is added to one or more process gases in a reaction chamber to form a plasma. One type of plasma based reaction chamber uses capacitively coupled plasma (CCP) to process the semiconductor wafer. FIG. 1 schematically illustrates a conventional CCP processing system that includes a processing chamber 2 having an upper portion 4 that flows one or more process gases into a reactor portion 6. The upper portion 4 includes a backing plate 8 having a plurality of apertures 10, a gas inlet 12 for introducing the process gases into the upper portion 4, and a plate 14 enclosing the upper portion 4. The one or more process gases flow into an antechamber between the plate 14 and the backing plate 8, and the gases then flow through the apertures 10 and into the reactor portion 6. The plate 14 may have channels 15 through which a fluid coolant can flow to provide a heat sink to remove heat from a first electrode 16 during plasma generation. The first electrode 16 or the backing plate 8 may include an electric heater 19 to heat the first electrode 16 before generating plasma. The first electrode 16 is positioned at the upper portion 4 and spaced apart from a second electrode 18 positioned in the reactor portion 6. The first electrode 16 illustrated in FIG. 1 also acts as a showerhead for distributing the process gases into the reactor portion 6. Conventional showerheads have hundreds to thousand of apertures 11, however only a few apertures 11 are shown for illustrative purposes in FIG. 1. One of the first or second electrodes 16 or 18 is powered by a radio frequency (RF) power supply 20 while the other electrode is grounded, or both of the electrodes are powered while a sidewall of the chamber 2 is grounded. The first and second electrodes 16 and 18 accordingly create an electric field that ionizes one or more of the process gases in the reactor portion 6 to form the plasma that can be used to deposit or etch material on the workpiece W.
CCP processes are often challenging because the characteristics of the plasma generated in the reaction chamber as well as the deposition or etching results depend on the electrode temperature, but it is difficult to quickly control the temperature of the first or upper electrode within a small range. For example, in conventional CCP chambers a thermal control unit controls the first electrode temperature, however typical thermal control units have large time constants and do not accurately maintain a set or constant temperature due to heat changes during processing (e.g., when the electrodes are biased on and off to form the plasma). Another problem associated with thermal control of the first electrode is that inconsistent electrode temperatures can produce inconsistent processing results. For example, with a fluorocarbon plasma, the amount of fluorocarbon polymer that is attracted to the first electrode, and therefore away from the wafer, is inversely proportional to the temperature of the first electrode. Conventional CCP chambers, however, have separate heating and cooling elements that increase the thermal impedance of the upper portion 4. Accordingly, conventional CCP reactors are subject to inconsistent starting temperatures and thermal fluctuations of the first electrode during plasma generation that can result in variability in the processing results.
Another problem associated with the thermal control of the first electrode is differential thermal expansion between hardware proximate to the upper electrode. The different components of the upper portion have different coefficients of thermal expansion, which can cause rubbing and stress during temperature cycling. This rubbing may produce particles that are conveyed by the process gas stream to the semiconductor wafer forming defects on the semiconductor wafer. Such non-uniformities and defects limit the utility of CCP vapor processing for forming very small microfeatures. Accordingly, a need exists for improved thermal control of the electrode and thermal management of the upper portion for consistent processing results in a CCP reactor.